The present invention relates generally to metal welding and forming devices and more particularly to a device in which tubular metal components are metallurgically joined (or mechanically formed) by energy acquired from a pulse magnetic field, otherwise known as magnetic-pulse welding.
Magnetic-pulse welding creates a full metallurgical joining of tubular metal components in a cold stage by applying a short impulse of mechanical force to the surfaces of coaxially pre-assembled tubular metal components to be welded. A predetermined magnetic impulse force created by an inductor assembly, forces the outer component against the inner component, thus forcing the molecules of the outer metal or metal alloy component to penetrate into the inner metal or metal alloy component, and create a full metallurgical joint in cold stage. Many different metals and metal alloys can be employed in the process, such as aluminum and copper, aluminum and steel, and aluminum alloys of different grades and tempers.
Methods of metal forming and treating using magnetic-pulse fields are well-known in the art. For example, the U.S. Pat. No. 2,976,907 to G. W. Harvey disclose three different designs of simple external inductors capable of forming or welding tubular workpieces. Generally, the simplest external inductor is a bar of conductive material, i.e. steel, copper, etc. formed in a loop which is connected to an energy source. The looped inductor is responsible for conducting an impulse current created by a special switching means (thyratron, spark gap, or other discharge means). The inductor concentrates a magnetic field inside of the loop's central opening in the period of duration of the initial impulse current. This field creates an inductive pulse current in the outer tubular workpiece which is repelled inwardly from the loop (external inductor) due to the electromagnetic interaction of the initial and inductive pulse currents and collapses against an inner component with predetermined force and velocity. As soon as these forces and velocity overcome a defined critical range, the molecules of the outer component metal penetrate into the metal of inner component producing a full metallurgical joint in cold stage.
While the prior art external inductors are adequate for the joining of relatively thin workpieces, there is a noted lack of external inductors which are capable of exerting sufficient magnetic fields for the joining of large diameter workpieces and workpieces of greater thicknesses. It is thus an object of the present invention to provide an improved external inductor device for magnetic-pulse welding which is capable of creating a more powerful and concentrated impulse of the magnetic field and a respective impulse of inductive current in the outer workpiece to develop more mechanical force and to perform at least 25-30% more deformation than a simple one piece external inductor. More specifically, the improved external inductor will consist of two separate components, namely an outer frame and an inner disk-insert, each fabricated from different metals, which split the responsibility for higher mechanical strength and more concentrated pulse current on the inner surface of inductor's central opening. The outer frame is preferably fabricated from steel to provide overall strength to the assembly, while the inner disk insert is preferably fabricated from a beryllium-bronze alloy which provides superior electrical conductivity around the inner perimeter of the inductor. A further object of the present invention is to improve the quality of the weld, or forming, in the area near the slot between the input and output contacts of the inductor. It has been found that inconsistent, i.e. non-uniform, welding or forming occurs in this slot area because the electrical current tends to seek the path of least resistance around the perimeter of the inductor structure, and the path of least resistance does not closely follow the slot. In other words, the pulse current will tend to follow an inverted U-shaped path rather than a more circular, i.e. Omega-shaped, path (.OMEGA.) around the inductor. Accordingly, the present invention seeks to concentrate the pulse current in the nearest proximity of the slot using symmetric oval openings within the body of the inductor loop. The openings are located in the path of least resistance and force the current to take a path which is closer to the slot, thus forcing the impulse current towards the inner surfaces of the inductor loop.
Still another object of the present invention is to extend the lifetime of such an external inductor assembly by providing a removable inner disk-insert which can be easily removed and replaced as needed.
Additional objects and advantages of the present invention will become apparent from the following description and claims.